Method for the direct modulation of an ultra-short wave transmitter



Aug. 8, 1950 M. PONTE ETAL METHOD FOR THE DIRECT MODULATION OF AN ULTRA-SHORT WAVE TRANSMITTER 2 Sheets-Sheet 1 Filed May 2, 194'! f 2% WW y 40 N R 6 Q 3M N\ a a m m w J m w P F A, mm T Li 5 NM 6 1L u m Q a W $2, H| g M l\ W a v m nuumuouun Emmmumumnumcuu a i NQMR a w. q 5% Aug. 8, 1950 M. PONTE ET AL ,5 8,37

METHOD FOR THE DIRECT MODULATION OF AN ULTRA-SHORT WAVE TRANSMITTER Filed May 2, 1947 2 Sheets-Sheet 2 [RI anion" fitmwos Paw- ANToI/ve' vise/v (E rem a WY @519 n is Patented Aug. 8, 1950 METHOD FOR THE DIRECT MODULATION OF AN ULTRA-SHORT WAVE TRANSMITTER Maurice Ponte and Antoine Jean Ortusi, Paris, France, assignors to Compagnie Generale de Telegraphic Sans Fil, a corporation of France Application May 2, 1947, Serial No. 745,378 In France March 22, 1946 Section 1:, PublicLaw 690, August 8, 1946 Patent expires March 22, 1966 14 'Claims.

It is known that-by modifying, the impedance of. the coupling slit of cavity resonator to the outer medium, in any rhythm, the resonator detuned in the same rhythm and the energy stored in the said resonator is also modified. If

be received and detected ina receiver.

the projection cabin and the screen.

slit.

wave. length in.

larly easy to produce by moulding).

2 vention which enables the film I to be slid in front of the slit 3 of the resonator 4, which latter may be of any desired shape. The film passes between. two parallel fiat parts 5 and 6', the latter terminating in two parts 7 and 8 which are The film I un- A high frequency tapping 5 a fraction of the said energ be tapped, it is posbent in the shape of a U having a depth equal sible thus to produce a centimetre wave which is to one quarter of the wavelength A used; this has modulated at the detuned rhythm, and can then the effect of preventing the incoming wave from leaking through the passages which are neces- The present invention. relates to a method of 10 sarily left open to allow the film to slide and inutilising the above mentioned principle. for the crease the quality factor of the resonator. direct modulation of an ultra-short wave trans- Following is a description of a few simple mitter, and, more particularly, for transmission methods according to the invention, which are of the sound, in sound kinematography, between given b way of non-limitative examples and which enable the principle mentioned hereinbe- According to the said invention, the impedance fore to be efficiently carried into practice. of the slit of the resonator is modified by passing In a first variant of the invention, which is in front of it, either, a sound-film strip or, more shown diagrammatically in Figure 3, the resgenerally, a strip fabricated expressly for the onator 4 is constituted by a guide element 9; it purpose of modifying the electric width of the is made as short as possible and at its two ends Accordingly, if such. a resonator be tuned are two conducting planes in which are formed to a certain wave length N), and. if. it be detuned two equal narrow slits 3- and 3'. by some means acting on the resonance frequency, winds in front of one of these slits 3 after the the amplitude of. the transmitted wave. varies. fashion of the arrangement of Figure 2. Then, This resulting impedance-frequency characterby approaching the critical quality factor, the istic T represents. the coefficient of transmission resonator enables one quarter of the power of the of the structure including the resonator at the oscillator to be transmitted with a low rate of To this end, use may be made, modulation; said oscillator may, for example, be for example, of a strip out out of a metallised a magnetron IQ located at one of the ends of the dielectric ribbon, the metallisation being preferguide 9, between a piston H and a slit I2, the abl effected in such a manner that its width guide 9 terminating at the other end in a small varies with the intensity of the sound: it is also transmitting horn 13. possible to use a strip of dielectric which is em- In a second variant of the invention, which is bossecl in such a manner that the thickness of shown diagrammatically in Figure 4, use is again the dielectric varies in proportion to the, sound made of a resonator 4 terminating in two slits l4, intensity (strips of plastic material are particul5 and placed in a guide 9 provided with a magnetron oscillator Ill at one end and a horn 13 If the quality factor of the resonator be sufat the other end. The coupling slit 3 with the ficiently great, mere. modification of the dielecfilm l is then placed in series with one of the sides tric constant of'the strip. of film at musical fre- 40 of the guide at a distance equal to one quarter quency, by means of the impression usually used, of the wavelength X from each of the slits l4 and is sufficient to modulate the wave at high fre- 15. In these conditions, a slight variation of the quency. For this purpose, for example, the sound impedance of the slit produces a quick variation track 2' (Figural) of the film I is passed in front of the resonance frequency. of the slit 3 of the resonator, the operative length In a third variant of the invention, which is of said slit being naturally limited to the width shown diagrammatically in Figure 5, the guide of the sound track. On the other hand, this couforming a resonator i is closed at one end and pling slitshould be fine enough-for the time taken the coupling slit 3 has the same arra ement as by an point of the film. to. pass across the slit in the first variant. to be of the order of the smallest musical period [6 in this case enables a portion of the moduused; for a frequency of' 10,000. C. P. S., for exlated wave to be fed to a transmitting aerial l5. ample, it is found that the width of the slit Finally, in a fourth variant of the invention, should be of the order of 0.1 mm. and if such the film can be made to pass in front of nara slit be arranged at right angles to the electric row slit which is dimensioned and shaped in acfield, resonator quality factorsof the order of the critical quality factor are obtained for av wave length of 10 cm.

Figure 2 shows a device according to the incordance with the device described in the U. S. patent application Serial Number 684,818,, entiled Guides for Radio-Electric Waves Associated with Elements for Regulating the Propagation of 3 Said Waves. Here the film is passed in front of the portion of the slit forming a capacity; this portion of the slit should, of course, be as narrow as possible.

Although the object of the present invention is not exclusively confined to the use of a modulated centimetric wave transmitter for the transmission of sound in kinematography, it is possible in this particular application to use, for example, the devices shown in Figure 6.

After it has passed through the projection appatus P, the film I passes through the sound detector, the elements of which are those of Figure 3. The receiver (on the right in Figure 6) comprises a diode or a crystal 18 which is fed by a small aerial l9 and is directly followed by a lowfrequency amplifier 20 which supplies a loudspeaker 2|. The said receiver is located behind the projection screen IT, or beside said screen if the same is metallic. The sound strip could, moreover, be one of the types referred to at the beginning of the specification, and its unwinding could be synchronised with that of the film carrying the pictures. Such a sound kinematography device has, inter alia, the advantages of obviating the use of cables between the projection cabin and the screen and of providing a sound detector which is free from the drawbacks of the usual photo-electric cell.

We claim:

1. A device for the direct modulation of an ultra-short electromagnetic wave comprising a resonator through which the wave passes and which is coupled to the outer medium, said resonator having a narrow slit provided in one of its walls a modulating strip element with means for passing it in front of said slit, said strip element and said slit being so arranged andiormed that the coefficient of transmission for the said wave varies in proportion to the desired modulation.

2. Device according to claim 1, in which said strip comprises the sound track of a sound film.

3. Device according to claim 1, in which said strip is a suitably cut out metal band.

4. Device according to claim 1, in which said strip is a strip of dielectric covered with a metallic deposit the dimension of which in the direction of the length of the slit varies in proportion to the sound intensity to be reproduced.

5. Device according to claim 1, in which said strip is a strip of embossed dielectric, the thickness of the dielectric varying in proportion to the intensity of sound to be reproduced.

6. Transmitter of ultra-short electromagnetic waves which are directl modulated by the use of the device according to claim 1, comprising the combination of a dielectric guide, an ultrashort Wave generator located within said guide the slit in front of which the strip passes is located in the wall of the guide at a distance from the planes of said conducting plates equal to one quarter of the wavelength, the wave which has passed through the strip being made to pass through an auxiliary guide portion a which is qlqsed atits end.- 4

8. Transmitter according to claim 6, in which the means for associating the strip with the slit in question comprise a U-shaped part, the bottom of the U being located opposite and at a short distance from the slit and being itself provided with a slit located in alignment with the first-mentioned slot, the arms of the U being of a length equal to one quarter of the wavelength used, so as to prevent the wave from leaking out of the guide through the spaces provided to allow the strip to move.

9. Transmitter according to claim 6, in which the slit in front of which the strip passes is one of the two slits provided in said conducting plates of the resonator.

l0. Transmitter according to claim 9 in which the slit is shaped like a U, the arms of which, acting as an inductive impedance in shunt, are parallel, and the bottom of which is at right angles to the lines of the electric field, the strip moving parallel to said arms, so that only the impedance of said bottom acting as a capacity in parallel is modified at the modulating frequency.

11. Method of transmitting at a distance a recording in the form of a band by direct modulation of the amplitude of an ultra short wave traversing a wave guide having in its interior and along the course of said wave a cavity resonator tuned to the frequency of said wave, comprising moving said band relatively to said cavity resonator so as to modif the impedance condition of the cavity resonator, and causing thereby a direct modulation of the amplitude of said wave in accordance with the recording on said band.

12. Method according to claim 11, in which said cavity resonator has a plurality of slits in its walls two of which are in the traverse path of said wave, and including the step of moving said band past one of said slits.

13. Method according to claim 12, including moving said band past a lateral slit not in alignment with said two slits.

14. Device for transmitting at a distance a recording in the form of a band, comprising a wave guide, means coupled to said guide for feeding in an ultra short wave of predetermined frequency, a cavity resonator located within said guide in the traverse path of said wave and tuned to the frequency of said wave, said resonator comprising two conductive diaphragms arranged perpendicularly to the longitudinal axis of the guide each provided with a fixed slit, the said slits being parallel, and means coupled to said resonator for causing said band to pass in front of one of said slits.

MAURICE PONTE. ANTOINE JEAN ORTUSI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Niunber Name Date 1,631,450 Andrews 1 June 7, 1927 1,859,665 Golden et a1 May 24, 1932 2,230,855 Wellmann Feb. 4, 1941 2,301,163 Koch Nov. 3, 1942 2,412,446 De Walt Dec. 10, 1946 FOREIGN PATENTS Number Country Date 309,834 Germany Nov. 18, 1918 

